Zinc electroplating baths and process

ABSTRACT

Bright electrodeposits are produced from an acid zinc bath containing at least one selected soluble organic carrier along with one or more conventional brighteners. The carrier improves the leveling of the bath and the texture of the deposit. Furthermore, it coacts with the brightener to obtain a bright ductile deposit over a wide range of current densities and temperatures. Suitable carriers are aliphatic diketone, dialdehydes and aldehydes/ketone compounds, various coffee base derivatives and selected six membered heterocylic compounds.

United States Patent [191 Skimin [451 Sept. 30, 1975 ZINC ELECTROPLATING BATl-IS AND PROCESS [75] Inventor: Carol W. Skimin, University [52] US. Cl 204/55 R [51] Int. Cl. C25D 3/22 [58] Field of Search 204/55 R, 55 Y, 43 Z, 44, 204/114, DIG. 2

[56] References Cited UNITED STATES PATENTS 3,778,359 12/1973 Popescu 204/55 R 3,787,296 l/l974 Hayashida et al 204/55 R FOREIGN PATENTS OR APPLICATIONS l,l25,584 8/1968 United Kingdom 204/55 R OTHER PUBLICATIONS Graydon E. Holdeman, Electrolysis of Zinc Sulphate Solutions at high current densities," pp. l4-l6,27&28, 1936).

Primary E.\'aminer-G. L. Kaplan Attorney, Agent, or Firm-James A. Lucas 5 7 ABSTRACT Bright electrodeposits are produced from an acid zinc bath containing at least one selected soluble organic carrier along with one or more conventional brighteners. The carrier improves the leveling of the bath and the texture of the deposit. Furthermore, it coacts with the brightener to obtain a bright ductile deposit over a wide range ,of current densities and temperatures. Suitable carriers are aliphatic diketone, dialdehydes and aldehydes/ketone compounds, various coffee base derivatives and selected six membered heterocylic compounds.

7 Claims, No Drawings BACKGROUND OF THE lNVENTION l. Field'of the Invention This invention relates to acid zinc electrodeposition and more particularly to a new and improved acid zinc electroplating bath and its use. The improvement includes the selected use of a family of carriers to improve leveling and texture of the zinc deposit and to coact with variousbrighteners to obtain a bright, ductile deposit over;a wide range of current densities and temperatures.

2.,Dis cussions of the Prior Art Alkaline zinc baths have dominated the field of zin electroplating for many years due primarily to the heretofore unsolved problems accompanying the use of acid zinc baths. Among these problems are inadequate brightness, inferior ductility, poor to moderatethrowing power, the production of a coarse, dendritic crystal structure, and the requirement that heat must be supplied to the plating bath for optimum use. Accordingly, the use of acid zinc baths has been limited to barrel plating and the continuous plating of wire, pipe and the like.

Recent concerns regarding toxicity; waste disposal and other problems associated with the use of cyanide and other alkaline zinc baths have create'drenewed interest in acid zinc baths.

Typically, acid plating baths have been based on, and named after, a suitable inorganic zinc salt such as zinc sulfate, zinc chloride, zinc fiuoborate, acetate, chloroacetate sulfamate or pyrophosphate, The bath usually includes a buffer such as the corresponding ammonium salt, one or more additives-to promote ductility, brightness, throwing power and covering power, and a surface active agent which'promotes refined crystal structure, reduces pitting and increases the solubility of said additives. These additives typically comprise a carrier such as benzoic acid or the salt thereof and a brightener which gives peak brightness over the entire surface of the deposit. The carrier and the wetting agent help to avoid misplate, improve the throwing power of the bath and promote uniformityof crystal structure.

Heretofore the carrier has consisted of an aromatic carbonyl compound, the most common of which has been benzoic acid. Despite continuing efforts to find other types of carriers for use in acid zinc baths, these efforts have not been entirely satisfactory.

SUMMARY OF THE INVENTION The present invention overcomes at least some of the drawbacks of the prior art zinc baths and resultsin the production of bright zinc finish by the use of an appropriate amount of a suitable carrier selected from the group consisting of:

a. aliphatic diketones, dialdehydes and aldehyde/ketone compounds wherein the oxygen atoms are attached to adjacent or to nonadjacent carbon atoms;

b. a coffee base derivative consisting of caffein, coffee and decaffeinated coffee; and. I I I c. a six membered heterocyclic compound'selected from the group consisting ofiniacin and l-cyclo hexene- 1 -one.

along with a wetting agent, brightener-s and other ingredients typically found in an acid zinc bath.

DETAILED DESCRIPTION OF THE INVENTION In more detail, this invention describes the improvement in acid zinc plating based upon the use of a novel carrier compound to be hereinafter described in detail. The carrier is used with brightening agents, including brightenersthat are well known in the art, to give a fully bright deposit. The brightener is usually present in an amount of between about 0.4 and 2 g/l.

The bath may be selected from the many available acid zinc baths containing inorganic zinc salts such as zinc sulfate, zinc chloride, zinc fiuoborate, etc., including various mixtures thereof. The salt is present in an amount that is adequate to supply between about 6 and about 45 g/l of zinc metal in solution.

The bath also contains a suitable non-ionic or anionic wetting agent such as an ethylene oxide adduct of a long chain alkyl phenol or alcohol having the formula where n is between 6 and 18 and x is between 8 and 30. The wetting agent is used in an amount of between 5 and 25 g/l to prevent pitting and 'to keep the additives in solution.

To prevent premature precipitation of the zinc, a complexing agent such as a source of ammonium ions, citrate ions, or ethylene diamine tetraacetic acid is added'to the bath in an amount of between 5 and 200 The bath may also contain a surplus of sulfate or chloride to increase conductivity, and a suitable buffer, such as boric acid, to maintain the pH of the bath in optimum range for plating.

The bath is typically operated at a temperature of between 10 and 45 C and preferably in the range of 20 to 30 C. Platingis conducted using current densities in the range of between 1 and 20 amps/square decimeter (a/dm Zinc may be deposited on ferrous metals, on copper and its alloys, on die cast metals and upon other metals such as nickel, cobalt or copper deposited on 'a metallic or non-metallic substrate.

The use of the unique carriers of the present invention in an acid zinc bath result in one or more of the following improvements:

a. The electrodeposithas a finergrain and improved texture. 1

b. The leveling properties of the bath are improved.

0. The carrier coacts with the brightener to'prolong the life of the solution.

d. The carrier improves the throwing power, i.e., the

ability of the bath to deposit in recesses; and

e. The carrier promotes uniformity in appearance over a wider current density range at higher temperatures, and over a greater pH span.

All of these improvements are obviously affected to a greater or lesser degree by the other ingredients in the bath and by other specific factors which are important in the operation of the bath and which are well known to the skilled electroplater.

The first group of carriers, the dialdehydes, keto aldehydes and diketones are characterized by aliphatic chain, saturated or unsaturated, with the oxygen atoms attached to adjacent or non-adjacent carbon atoms. This group is represented by compounds of the formula I Glyoxal Pyruvic Aldehyde The ductility of the deposit obtained from a bath containing glyoxal is good. As the carbon chain increases in length, however, the ductility gradually decreases and is only fair where diethyl vfumarateis used as a carrier. These carriers are typically used in an amount of between about 1 and about 60 ml/l in the plating bath and are capable of giving a uniformly lustrous finish without a brightener and a fully bright finish when used with a brightener.

These compounds have been found to be useful with a wide variety of brighteners including the various.thiophenes, thiazoles and furan compounds described in copendingapplication Ser. No. l0,090, filed of even date herewith, various aromatic carbonyl compounds such as benzalacetone, benzophenone. benzol acetonitrile and aceto coumarin, and non-aromatic, unsaturated compounds such as citral.

The second group of carrier compounds constitute coffee or derivatives thereof which can be used in a conventional acid zinc plating bath to give a uniformly lustrous deposit, or lwhen used with a conventional brightener such as benzalacetone, to give a fully bright deposit. In this group are included instant freeze dried coffee such as the coffee sold under the trade name MAXWELL HOUSE Coffee, decaffeinated coffee from which 98 to 99% of the caffeine has been removed and sold commercially under various trade names such as SANKA, DECAF and BRIM, and caffeine, the formula of which is C l on H C YN Generally the effective ran ge-of this group of carriers is between 0.75 g/l and 2 g/l.

Any of these coffee based derivatives, when used as a'carrier along with a brightener such as benzalacetone, acetothiophene, acetocoumarin, benzophenone, or thienyl methylethynyl carbinol, give a fully bright deposit at low, medium and high current densities.

The last group of carriers is characterized by a six member heterocyclic ring'and includes the following compounds:

Niacin Z-cyclohexene- 1 -one Either of these compounds, when added in an amount of between 0.5 and 1 g/l to a standard acid zinc plating bath, serves to increase the throwing power, texture and luster of the deposit. These compounds have been found to be suitable when used with various brighteners such as:

Thiophene aldehyde I I fi-H Benzophene thienyl methylethynyl carbinol The ductility of the deposits plated from a bath containing 2-cyclohexene-l-one is outstanding.

The following examples are presented to more fully illustrate the present invention but without placing any limitation on the scope thereof.

EXAMPLE I An acid zinc electroplating bath was prepared as follows: Y

ZnCl- 100 g/l NH C1 185 g/l Wetting Agent* I 1.25 g/l (OCH CH- -),,,OCH COOH sold commercially as Akypo ()P 190.

The following tests were conducted using brighteners in conjunction with either sodium benzoate (10.2 g/l) or glyoxal (12 g/l) as carriers. Deposition was carried out in a one liter bath on bent 3.8 X 15.25 cm brass cathodes using bagged zinc anodes. The bath was maintained at room temperature and was mechanically agitated during deposition which was conducted at 1.5 amps for minutes.

a. 0.5 to 1.0 g/l benzalacetone produced fully bright deposits using either sodium benzoate or glyoxal as the carrier.

b. 1.0 to 1.5 g/l of acetothiophene likewise produced bright deposits from baths using either carrier.

c. 1.0 g/l of 3-acetocoumarin gave a fully bright deposit with glyoxal and with the benzoate.

d. A mixture of 12 g/l glyoxal and 10.2 g/] sodium benzoate without a brightener produced no brightening effect, the appearance being similar to that obtained from a bath containing one of the carriers without a brightener.

EXAMPLE 11 Additional panels were plated from the acid bath of Example I using 0.5 g/l glutonic dialdehyde as a carrier in place of the sodium benzoate and the glyoxal. A fully bright deposit was produced when used with each of the brighteners, benzalacetone, 2-acetothiophene and 3-acetocoumarin.

EXAMPLE 111 Under the same plating conditions and using the same bath used in Example I, fully bright deposits were obtained using the following carriers in conjunction with 1.0 g/l benzalacetone as the brightening agent:

a. 0.75 1.0 g/l Instant MAXWELL HOUSE Coffee b. 0.75 2.0 g/l Instant SANKA Coffee 0. 0.01 1.0 g/l Caffein d. 1.0 g/l 2cyclohexene-1-one Although these examples are all limited to zinc chloride/ammonium chloride baths, the invention is applicable to ammonium-free baths and other types of acid zinc baths as well. Furthermore, good results are obtainable when two or more of the carriers of this invention are used together in an acid zinc bath.

1 claim:

1. An aqueous acid zinc electroplating bath containing at least one acid salt source capable of supplying between about 6 and 45 grams per liter of zinc ions in solution, between about 0.4 and 2 grams per liter of a brightening agent, and between 5 and 25 grams per liter of an anionic or non-ionic wetting agent, said bath improved by the inclusion of between 1 and 60 milliliters per liter of a compound having the formula wherein X is absent, or is a vinylene group or a lower alkylene group having from 1 to 3 carbon atoms, and wherein R and R are, independently of one another, hydrogen, or a lower alkyl or alkoxy group having from 1 to 3 carbon atoms.

2. The bath according to claim 1, wherein the compound is selected from the following group glyoxal, pyruvic aldehyde, glutaric dialdehyde, acetyl acetone and diethyl fumarate.

3. A method of electrodepositing a bright, level finegrained zinc layer on a conductive substrate from an aqueous zinc plating bath containing between about 6 and 45 grams per liter of zinc ions in solution, a brightening agent present in an amount between about 0.4 and 2 grams per liter, 5 to 25 grams per liter of an anionic or non-ionic wetting agent, and a carrier selected from the group consisting of:

a. l 60 milliliters per liter of a compound having a formula wherein X is absent, or is a vinylene group or a lower alkylene group having from 1 to 3 carbon atoms, and wherein R and R are, independently of one another, hydrogen, or a lower alkyl or alkoxy group having from 1 to 3 carbon atoms;

b. 0.75 2 grams per liter of a coffee base derivative selected from the group consisting of caffein, coffee, and decaffinated coffee;

0. between 0.5 and 1 gram per liter of Z-cyclohexenel-one, and

d. mixtures thereof, comprising passing current through the bath from an anode to the conductive substrate as a cathode at a current density of between 1 and 20 amps per square decimeter while maintaining the bath at a temperature of between 10 and 45 degrees Centigrade.

4. The method of claim 3 wherein the carrier is a coffee base derivative.

5. The method of claim 4 wherein said brightening agent is selected from the group consisting of benzalacetone, acetothiophene, acetocoumarin, benzophenone and thienyl methyl-ethynyl carbinol.

6. The process of claim 3 wherein the carrier has a formula and is selected from the group consisting of glyoxyl, pyruvic aldehyde, glutaric dialdehyde, acetyl acetone and diethyl fumarate.

7. The method of claim 3 wherein said brightening agent is selected from the group consisting of acetothiophene, acetofuran, benzalacetone and thiophene aldehyde. 

1. An aqueous acid zinc electroplating bath containing at least one acid salt source capable of supplying between about 6 and 45 grams per liter of zinc ions in solution, between about 0.4 and 2 grams per liter of a brightening agent, and between 5 and 25 grams per liter of an anionic or non-ionic wetting agent, said bath improved by the inclusion of between 1 and 60 milliliters per liter of a compound having the formula
 2. The bath according to claim 1, wherein the compound is selected from the following group glyoxal, pyruvic aldehyde, glutaric dialdehyde, acetyl acetone and diethyl fumarate.
 3. A METHOD OF ELECTRODEPOSITING A BRIGHT, LEVEL FINEGRAINED ZINC LAYER ON A CONDUCTIVE SUBSTRATE FROM AN AQUEOUS ZINC PLATING BATH CONTAINING BETWEEN ABOUT 6 AND 45 GRAMS PER LITER OF ZINC IONS IN S3LUTION, A BRIGHTENING AGENT PRESENT IN AN AMOUNT BETWEEN ABOUT 0.4 AND 2 GRAMS PER LITER, 5 TO 25 GRAMS PER LITER OF AN AIONIC OR NON-IONIC WETTING AGENT, AND A CARRIER SELECTED FROM THE GROUP CONSISSTING OF: A. 1-60 MILLITERS PER LITER OF A COMPOUND HAVING A FORMULA
 4. The method of claim 3 wherein the carrier is a coffee base derivative.
 5. The method of claim 4 wherein said brightening agent is selected from the group consisting of benzalacetone, acetothiophene, acetocoumarin, benzophenone and thienyl methyl-ethynyl carbinol.
 6. The process of claim 3 wherein the carrier has a formula
 7. The method of claim 3 wherein said brightening agent is selected from the group consisting of acetothiophene, acetofuran, benzalacetone and thiophene aldehyde. 